/*
 * @(#)$Id$
 * 
 * Copyright 2006-2008 Makoto YUI
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 * 
 * Contributors: Makoto YUI - initial implementation
 */
package jacky.lanlan.song.concurrent;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * 
 * @author Makoto YUI (yuin405+xbird@gmail.com)
 */
public final class AtomicPseudoRandom {

	private final AtomicInteger seed;

	public AtomicPseudoRandom() {
		this((int) System.nanoTime());
	}

	public AtomicPseudoRandom(int seed) {
		this.seed = new AtomicInteger(seed);
	}

	public int nextInt(int n) {
		while (true) {
			int s = seed.get();
			int nextSeed = calculateNext(s);
			if (seed.compareAndSet(s, nextSeed)) {
				int remainder = s % n;
				return remainder > 0 ? remainder : remainder + n;
			}
		}
	}

	private int calculateNext(int s) {
		s ^= s << 6;
		s ^= s >>> 21;
		s ^= (s << 7);
		return s;
	}

}
